Technical *Easy & Cheap* Home made TOP DEAD CENTER (TDC) Tool HOW TO.

This Idea is nothing new... but I had to make one in the shop today, got to thinking about all the great "How-to" tech articles on the HAMB and did not find anything on making a TDC Dial Indicator in a search.. (However, I'm still new to the NEW format and could be totally missing it!)

Anyways, this tool works BEST on Early Bangers, a lot of Inline engines, and anything with a spark plug located directly over top the Piston, HOWEVER.. I HAVE USED THESE INDICATORS on such engines as a Chevy Small block and it worked fine for me!

***The Engines we build are the Legendary OFFENHAUSER Racing engines, and Harry Miller Engines... Pictured here is a 270 Offy**

Furthermore, I UNDERSTAND that different engines require different size Spark plugs, and ONE TOOL will not fit all here, but if you build a lot of ONE CERTAIN type of engine, fabricating one of these for your self would help in many ways during assembly, setting timing, maintenance, and tuning. ...and maybe seeing how I do it, will spark an idea of how YOU can do it.

Lets get started:

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1. Buy a cheap Dial Indicator. I found this one in the MSC Supply catalog for $19.00.. It happened to be on sale and it cost me $9.00 when it was all said and done. (I know it's a cheap CHINA rip off and you should ALWAYS BUY AMERICAN!!! ...but I'm a Baller on a budget.)

2. For my application (Offy) the Early 2 piece Champion Spark plugs work PERFECT. If your engine is a later model and uses one piece Spark plugs... you will need to bust the porcelain center out, DRILL the entire center of the plug out, and put a set screw in the side of the plug, or Weld it to your FIXTURE SLEEVE. (see step #4 )

3. Dissasemble the Spark plug or drill out the center. The size is determined on the O.D. of your FIXTURE SLEEVE you are going to machine.

4. In the case discussed here (Early Champion Spark plugs) the FIXTURE SLEEVE you will need to make, mimics the Porceleon core and will clamp into the Original 2 piece Champion Spark easily. Measure the Base, and duplicate. I have found that making this Fixture 2" long works best in Clearance issues on most engines.

5. The center hole in your fixture sleeve needs to fit the O.D. of the Dial indicator BASE. In my case, with the cheap CHINA model it was 3/8 exactly. At the top of the fixture sleeve drill and tap for an #8-32 Set screw. This set screw will not only lock the Dial indicator into place, but make it adjustable UP & DOWN the length of the Indicators base, as well as you'll be able to rotate the Indicator any direction you need to view it once the Spark Plug base is tight in the Spark plug hole.

6. ALL DIAL INDICATORS have changeable Stems.. you can stack and make ANY length you may need for your application.

7. DONE. Insert the indicator into the Block or Head, slowly rotate the crank up and watch as the indicator will turn one direction.. then go the other. THAT CHANGE IN DIRECTION IS YOUR TOP DEAD CENTER. Set the needle on the exact "Direction change point" and rotate ZERO around to that spot. Now you are "Zeroed out" at TDC. From here you can figure out TIMING DEGREES without a timing plate or Timing marks on your Flywheel.

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I know there is a TON of variables here, and other ways to do it.. and you can probably BUY one of these tools on-line.. But in my case (as with most of Hot Rodding) a Dial Indicator for a 270 Offenhouser wasn't in stock at AUTO ZONE. Plus, its just WAY COOLER to make your own tools.

Joshua Shaw

 

Great idea! Nice tech too.

 

nice tool and quite useful but some are going to disagree with your method, based on TDC dwell ("got to go both ways....")

 

I have a video showing it's use, but I can't figure out how to upload it on the new forum... Any help?

...as for people disagreeing with my methods.. That's quite common. I quit listening a LONG time ago.

 

Posted using the Full Custom H.A.M.B. App!

 

Nice work Josh! Now how do I get my hands on the wheel of that Offy powered Hot Rod? Probably cost just a wee bit more than $19.00 right! Cool tech! THANKS!

 

In our application (Offys) we use this method to find TDC to set our Gear Tower timing to drive the over head cams, and to install the cam timing correctly. It WORKS PERFECT FOR US.
If this method won't work for your application,.. Don't Use It.

 

Josh you found top center not top dead center. Top dead center would be the mid point between where the indicator stopped moving & where it began to move again. As you say its not going to affect the valve timing because the difference is not enough to affect a change in the gear placement or tooth engagement. As a former resident of southern Ohio & involved in racing there in the 59s&60s thank you for the sprint car thread. WAW

 

Piston stop and degree wheel. Tried, True, and dead-nuts accurate.

 

THANKS! I'm so happy to know that the way we, and countless other Indianapolis Crew Chiefs, plus other Old time Engine builders have FOUND TDC, set our timing, and assembled engines that run perfectly, and exactly where we want them the first time, have been doing it TOTALLY WRONG FOR YEARS!!! I should post on here more often, so I can learn how to do it like the pro's, and not the OLD TIMERS that teach me first hand.

Fella's, I completely understand and KNOW ABOUT everything you pointed out, and agree with it. If ya'll NEED to assemble YOUR engines with Degree Wheels, Piston Stops, etc.. That's fine!! Have at it! I'm showing people another way that works.

 

I was 'juggling' a cam in the shop a few years back, Friday late afternoon. Discovered my assortment of cam bushings had been rifled by my no-account brother...Drove to the local "speed shop", my friend Don wasn't around but he had hired a couple of red-hot counter jockeys who proceeded to tell me what I was doing was bullshit.
These 2 'tennis-shoe M.F.s' knew so much that it was preposterous that a lowly subject such as I should be debating the universally know fact that cam timing inside 6 degrees was simply a moot point.
"If you have 2 degree bushings, please sell them to me, otherwise tell your boss that he'll be getting a phone call from me..." and gave them my card.
They produced the bushings, but cautioned me that I was wasting my time...
I replied that wrist pin offset and bearing clearances had forced the minimal increments. (I hoped they thought about that one...)
(Falcon George's post reminded me of the event...)

 

Anyone racing who is setting TDC like this, all I can say is OMG. This is not an appropriate way to set TDC, if you think so, have at it. You could get there with a dial indicator but it takes a lot of work and with a loss of accuracy, so why? TDC is located with a dead stop and an indexing plate (degree wheel) and any engine builder would know this.
Edit: It would help if I could learn to check my spelling!!!

 

I assume you guys don't know who Josh is and I'll leave it at that.

 

I'm not disagreeing with you that using a degree wheel and splitting the difference between the 2 points is whats considered the closest you can get (I would think piston rock could skew an absolute reading) But I'm also not going to tell a guy that builds and restores million dollar Miller and Offy Indy Cars (some of them from almost nothing, meaning making most of the parts from scratch) that he's full of shit either.

 

He's not full of shit, and you can locate TDC with a dial indicator, but that is not an easy way to go it and it's much more involved than his post indicated. With his setup if you checked the dial to some setting off of TDC several times from both directions of rotation and split the difference it would work fine, I've seen it gone that way. But seems a lot more complicated than doing it in a more conventional manner. I have been building race engine sense the 60s and know a little about it myself as do a lot of other individuals who were commenting on his method. All of us make errors in what we post from time to time and there is nothing wrong with being corrected when it occurs. What he was attempting to post may have been fine, but the way it ended up was misleading and factually incorrect IMHO.

 

I can tell you all about that!!! Me and 4.6 Ford engines have had several run-ins. A few little degrees allows you to pull the heads and replace the valves you bent. Damn them engines are touchy! If you want a quick lesson on how important TDC is and what a few degrees mean, work on a few of them.

 

Agreed.
Cosmo

 

You fellas are a riot! I see the new HAMB hasn't lost it's luster from 15 years ago when I used to post on here.
First off, thank you for all your input. I agree with it all! Your all correct.
Jseery- thank you for replying in a non-condensing way. I appreciate it.
Falcongeorge- I have numerous Dial indicators, calipers, and precision measuring instruments of all kinds, most handed down to me by old timers and my late grandfather... However, none I wanted to DONATE PERMENENTLY to make this ""cheap "carry to the races" easy checker. (Plus, the point of this was for the "Home-builder Hot Rodder on a budget")
Which brings me to my next point.. Offenhousers, and our vintage Injected Chevy Sprint car engines DO NOT HAVE an external Harmonic Balancer with timing marks like NORMAL engines.. Nor do we run a Fly wheel that we can pick up timing points either. When WE are at the track, and making adjustments or repairs THIS IS HOW WE GET TDC when and if we need it.
It's a cool little tool I thought I'd share with y'all.. Did I mislead you (3 or 4) Into thinking I was stating that this was the BEST and ONLY way to do it? Perhaps. If so, I'm sorry you misunderstood me.
To the huys that saw this and thought "that's a cool idea I can do at home, and use it" KICK ASS! You got it.. To you other couple fellas that spent the entire day and Friday night typing long drawn out boring ass replies in the attempt to make your self sound really smart, and like an expert.. GET YOUR ASS OUT IN THE SHOP AND GET TO WORK!

(I tried to delete this entire thread cause it was obviously accepted and digested wrong.. But I don't know how. I'm not a regular here... )

J S

 

Joshua, that is a neat little rig, and probably works great at the track, however if you are using that exact method to do your initial assembly you could do better, if you don't factor in the dwell you won't know for sure. Even famous people can learn, if they stop beating there own chest and keep an open mind. There is very much a difference between top center, and top dead center.

 

Great track tool...thanks for posting it.
Got a chuckle out of your comment...couldn't said it better myself. A few guys on here "pick shit with the chickens" all day long. Now, I gota get back to block sanding...boring!

 

Great idea! I may attempt to make one since I am not smart enough to use a degree wheel. Also, this thread is exactly why I simply lurk here and not post much. I am afraid of an internet attack.

 

Although a bit different reason for doing so, but to give credence to Joshua's procedure & the mechanics of it, the idea definitally came into use on my 331 Hemi.
After assembling the heads, etc on the engine and visually checking the position of "TDC" on the HB and comparing with a thin rod inserted into the sparkplug hole, the scale on the HB was found to be about 19º off due to slippage over time.....only 58 years.

So, nothing to start with.......... a degree wheel would be of no use at this juncture.

The HB was replaced with a new one that fit a Mopar 360 and which does not have the same keyway alignment.

I built exactly what Joshua did and used it to establish the new timing marks on the HB.
The crank was rocked forward and back and the difference(s) split to get a "0". IIRC, the 360 HB was off 90º
From there, it was just a matter of laying out successive marks for 2º divisions either side of the "0"

Worked for me.

gatz

 

Ok, for the folks who care, Joshua's method may work fine for what he is working on and for you if you are doing something similar. It will not establish TDC and I am sure he is aware of that. So, you had been warned. If you are interested in somewhere near TDC (say within 3 to 6 degrees) this works, but it will not establish a TDC if that is what you need.

 

Joshua: "THAT CHANGE IN DIRECTION IS YOUR TOP DEAD CENTER. Set the needle on the exact "Direction change point" and rotate ZERO around to that spot. Now you are "Zeroed out" at TDC".
gatz: "The crank was rocked forward and back and the difference(s) split to get a "0".

Maybe you don't see the difference, but it is important! Sure you can use a dial indicator (or just about anything) it is the procedure that is important.

 

stop it....I have a soar back and laughing like this makes it worse!

 

It is sad that people want to debate in place of learning. So be it, guess I have to agree with some others on here, there are folks that just are not interested in learning how to do things. Rick says Joshua is "spot on" then says he (Rick) uses a dead stop. This is just unbelievable! Well, I give up.

 

Well, kinda.....when you check a bore for size, you need to find the max setting of the gauge; and "rocking" the gauge while slightly moving the points or anvils (for lack of a better name) until the gauge passes through. Takes a bit of practice.
If you were then to put the gauge back into the bore, it should not just merely slip on in, ...it should have the same feel as the first "reading".... a slight bit of resistance at the peak or max measurement..
If it doesn't, then you need to repeat the procedure to get a repetitive feel or measurement. Just to clarify, this is when using a gauge with 2 opposing anvils or points; like Starrett Hole Gauges. If a 3-point gauge is used, the same "rocking" motion would still apply, but there shouldn't be any sideways movement at all. The 3-point gauges are the most accurate, but can be expensive as they are direct reading. The 2-point are just transferring the measurement and read with a mic. The 3-pt gauge would also give you an idea of out-of-roundness if present.

As re the TDC issue;
To me, "rocking" the gauge (actually the engine crank) means to find that central point where the piston stops moving by rotating from either direction. You could scribe some temporary lines on the HB, and these can be at say 0.005 or 0.010 either side of the nominal O on the dial indicator obtained by rotating one direction, then reverse the rotation, coming up on the other side of O to the same increment amount on the dial indicator. (some indicators are marked + & - on either side of O.
When looking at the scribed lines on the HB, you'd see a gap between them. Keep checking with the dial indicator and compare the scribe lines so that you're satisfied that you've measured correctly. The midpoint between the scribe lines would be TDC

 

I have been watching this one and have reread this and the only thing I can figure is that using this method you will have the crank on the downward side of the TDC that I think would just always have you timing just a little retarder and if you always use this method and you play with cam timing and ignition timing your timing deg may be different than someone that uses a dead stop to find TDC.
Say I use a dead stop and I have my cam advanced 12 deg It may be 14 with the dial indicator method.
Shit I dont know my head hurts now.

 

Sounds like a bunch of 'rappers' telling Sinatra that he doesn't know music...'nuf said.

 

This is the method I use on my vintage Chevy II powered USAC midget. I agree it only gets you within a 2-3 degrees of exact TDC, but it works. Think about it, your at the track, you mag craps out and you have to change it out. You have no crank snout sticking out of the motor, you have no flywheel. This is the only way to do it without pulling a head. Plus these motors are not tuned with a timing light anyway. You set initial timing then tune with the motor running by temp, plug readings, throttle response, etc. Its an art to get these things running like a fire breathing dragon, not just a timing light.